Automatic load and vacuum sensitive exhaust hood spray system

ABSTRACT

In order to provide temperature control for the exhaust hood region of low pressure turbines, the exhaust hood sprays are activated in response to measured load and steam exhaust pressure. During start-up of the generator, the sprays always are turned on. During normal operation, the status of the sprays depends on the relative amounts of load and vacuum pressure. If the load is less than 10 percent, the sprays are always on, and if the load is greater than 25 percent, they are always off. In the range between 10 and 25 percent load, the status of the sprays depends both upon load and vacuum. In that range, if the vacuum is less than 26 inches Hg., the sprays will be on, and if the vacuum is greater than 28 1/2 inches Hg., they are off. Between 28 1/2 and 26 inches vacuum pressure for the 10 percent to 25 percent load, the status of the sprays depends upon a combination of the two factors.

United States Patent 1191 Cohen et al.

1111 3,885,822 1451 May 27, 1975 [54] AUTOMATIC LOAD AND VACUUM 3,151,250 $1364 carlsolrll 415/116 X SENSITIVE EXHAUST HOOD SPRAY 3,601,617 1 71 DeMe O et al. 290/40 C SYSTEM 3,628,042 12/1921 Jacobus 290/40 R 75] Inventors: Albert Cohen, Wallingford; Frank Primary Examiner Robert S. Ward JR 131} 3:12: 2 tfl gn gs il gkigsg an Attorney, Agent, or FirmH. W. Patterson of 57 ABSTRACT [73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, In order to provlde temperature control for the exhaust hood reg1on of low pressure turbmes, the ex- 1 1 Flledi June 21, 1974 haust hood sprays are activated in response to mea- [21] Appl. No.: 481,934 sured load and steam exhaust pressure. During startup of the generator, the sprays always are turned on.

During normal operation, the status of the sprays de- [52] US. Cl 290/1 R; 290/40 R; 290/52; pends on the relative amounts f load and vacuum 415/1 16; 239/1; 239/289; 415/1 ressure. If the load is less than 10 percent, the sprays [5 hit. Cl. are always n and the load is greater than per- 1 1 Fleld of Search 415/175, 117? cent, they are always off. In the range between and 290/4 40 40 l R, 1 A, percent load, the status of the sprays depends both 239/13 289 upon load and vacuum. In that range, if the vacuum is less than 26 inches Hg., the sprays will be on, and if 1 References Clted the vacuum is greater than 28 /1 inches Hg., they are UNITED STATES PATENTS off. Between 28 /2 and 26 inches vacuum pressure for 873,041 12 1907 Gray 415/116 x the 10 percent to 25 P n l9ad, the status f the 1,400,813 12/1921 Graemiger 415/116 UX sprays depends upon a combmation of the two factors.

1,824,893 9/1931 Holzwarth 415/117 2,916,635 12/1959 Nicita 290/ c 41 Clalms, 4 Drawlng Flgures 1 a 123 i V 2 101 t I 11 1i 11 1111' 11 I .1

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AUTOMATIC LOAD AND VACUUM SENSITIVE EXHAUST HOOD SPRAY SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates'to the generation of electrical power, and more particularly, to the enhancement of generation reliability by control of temperatures at the last turbine output stage.

2. State of the Prior Art In conventional power generating system, it is common to utilize a succession ,of three turbines, with steam being circulated in order, from a high, intermediate, and low pressure set of turbines. Typical1y,,the high pressure turbines are the smallest in size and the low pressure turbines are the largest. Also typically, steam is introduced into the center part of the bore of oppositely facing dual low pressure turbines, and exits at the outer portion of either side thereof. In that region, exhaust hoods contain and direct the flow of steam, to a condenser where water is formed and pumped back to the boiler.

Dur to the large size of the low pressure turbines, there is often produced large amounts of heat due to friction of the turning blades with surrounding steam. This friction is commonly known as windage. In particular, the amount of heat produced from windage is dependent on the vacuum in the region of the exhaust hoods. In accordance with modern design trends, which feature cooling towers and a general trend toward operation with a poorer vacuum, windage heat may be sufficiently high to bring about inefficient operation an physical damage to the equipment.

A common approach to limiting the accumulation of heat in the exhaust hood region of low pressure turbines has been to provide hood sprays which supply a cooling fog to mix with hot steam in the exhaust hood area and thereby regulate the temperature. The most common approaches to control of the hood sprays have been to use either a set of fixed speed-related and load related set points for turn-on in the range of 600 rpm. and turn-off, at approximately percent load or a direct thermostatic control, typically seeking to maintain the temperature below 175 F. v

The fixed set point scheme involves obvious disadvantages relative to flexibility and adaptation to changing operational conditions.

In most cases, direct thermostatic control of heat in the areaof the exhaust hoods has also been inadequate, principally during times of low load upon the turbine generator, or when the turbine generator is being brought up to speed during start-up. During these times particularly, the temperture stabilizing effect of steam through the turbine is absent,,and windage heat builds up to excessive levels. This effect is further accentuated if the exhaust vacuum is relatively poor.

It is accordingly a principal object of the present invention to provide apparatus and methods for the control of hood sprays in turbine generators. It is a more particular object to provide such method and apparatus which prevents build up of unwanted heat during times of start-up and low load and/or poor vacuum.

SUMMARY OF THE INVENTION The present invention fulfills the foregoing objects by providing a hood spray control system which is responsive both to load and to vacuum in the exhaust hood area of turbine generators. In accordance with the principles of the present invention, the hood sprays are always turned on for very low loads, which include the no load start-up conditions. Above a predetermined level, both the load and the vacuum are considered, the spray energizing signal being inversely proportional to the load and directly proportional to vacuum for a specified range of each. Above the respective load and vacuum ranges, the sprays may either be disabled, or alternatively, may be energized in accordance with conventional techniques.

In an illustrative embodiment, transducers sense the present generator load and the exhaust pressure. The load percentage is compared with a first reference, and if the reference is larger, the hood sprays are energized. Both the measured load and the measured vacuum are respectively scaled to facilitate interaction with one another. The scaled load and vacuum signals are combined and compared with a second reference. Again, whenever the combined signal is smaller than the reference, the hood sprays are energized. In preferred embodiments, the hood sprays are automatically turned on for all loads less than 10 percent, and the ranges 10 to 25 percent load and 28 /2 to 26 inches Hg. vacuum form the inactive range with the second reference.

It is a feature of the present invention that excessive temperature at the exhaust stage of low pressure turbines is avoided. In particular, both load and vacuum pressure factors are utilized to achieve interactive control. Moreover, accurate control is achieved for low load and imperfect vacuum conditions where the heating effects of windage overcome the temperature stabilizing influence of steam. These and other features may be seen from consideration of the figures in conjunction with the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows symbolically the exhaust hood region of a dual low presure turbine, with hood sprays;

FIG. 2 shows in block diagrammatic form an illustrative embodiment of the present invention;

FIG. 3a through 3e show waveforms for the embodiment of FIG. 2; and

FIG. 4 shows a schematic diagram of an analog circuit embodying the principles of the present invention.

DETAILED DESCRIPTION FIG. 1 shows a stylized version of a low pressure double flow turbine typical of those used in the art. A centrally located rotor 101 connects the low pressure turbine shown with intermediate and high pressure turbines, and a generator, as desired. The view shown in FIG. 1 is from the top, with a cutaway in the region of the rotor. It is to be understood that the apparatus shown in FIG. 1 is simplified considerably, and that actual turbines involve machinery of considerably greater detail and complexity. However, the detail shown in the top view of FIG. 1 has been simplified to illustrate the principles of the present invention. Since the turbine is cylindrical in shape, the structure shown at the bottom of FIG.,1 is identical to that shown at the top.

The rotor 101 is mounted on bearings and 131, and the actual double flow turbine is isolated from ambient conditions in the region of the rotor by seals 132 and 133, thereby forming a steam tight chamber within the turbine. The turbine housing is partially formed by the steam exhaust hoods, shown generally as 128 and 129. The hoods 128 and 129 are fixed relative to the rotor 101, and are connected to central structural portions shown generally as 123. In reality, the large solid apparatus shown as 123 involves considerable structural complexity, but none of which is relevant to the principles of the present invention.

As is common in the art, the turbine of FIG. 1 includes oppositely facing separate turbine units, radiating outwardly from the steam inlet 122. Then. from the steam inlet at 122 to the hoods 128 and 129 are respective pluralities of blades, some of which, 102 through 111, are affixed to the rotor 101, and others of which, such as 112 through 114 and 119 through 121, are affixed to the stationary portion 123 of the turbine. The steam enters the turbine at steam inlet 122 and from there passes outwardly in both directions through the stationary and moving blades toward exhaust hoods 128 and 129. The force of the steam passing through the blades causes the rotor 101 to turn, thereby facilitating production of electricity by generator means, not shown. As the steam reaches the exhaust hood regions 128 and 129,"it is channeled around flow guides 124 and 125 and down through a bottom exhaust, not shown, where it is directed into condenser apparatus, not shown. In the normal course, a partial vacuum is set up in the exhaust hood regions 128 and 129.

Also shown stylistically in FIG. 1 are the hood sprays 126 and 127, which expel a cooling water spray into the exhaust hood regions 128 and 129, thereby providing temperature stability, in those regions.

As is explained in considerable detail hereinafter, the principles of the present invention involve carefully controlled operation of the sprays 126 and 127 into the hood regions 128 and 129 in response both to the measured load on the generator and the partial vacuumin the region of the exhaust hoods 128 and 129.

FIG. 2 shows in block diagrammatic form an illustrative embodiment of the present invention. The waveforms of FIGS. 3a through 3e depict operation of various blocks of the FIG. 2 embodiment, and together illustrate the operational effect of the principles of the present invention.

In FIG. 2, a turbine generator 210 is shown symbolically. The turbine generator block 201 represents a plurality of turbines, at least the low pressure segment of which includes exhaust hoods and hood sprays. The hood sprays are energized by one or more on-off relays 204. Located appropriately in the turbine generator are transducer probes 202 and 206 which respectively sense the present values of operating load and partial vacuum in the exhaust hood region of the generator 201. The load and vacuum transducers 202 and 206 produce voltage signals p and h The time variant load signal p is given in terms of percentage of peak load, and the partial vacuum h,. is represented in terms of inches of mercury, commonly designated in. Hg. Of course, the signal p and h are rather arbitrary in terms of absolute signal magnitudes, it being important only that they interact properly with one another and with the various reference voltages throughout the system.

The percentage load p is coupled to a comparator 203 where it is compared with a first reference voltage, V,,,, from a reference voltage source 212. The amplitude of the first reference voltage represents the load cut-off below which the hood sprays are always turned on. In preferred embodiments, the first reference V from source 212 corresponds to IO percent load, such that below that value, the sprays always will be turned The transfer characteristic of the comparator 203 is shown in FIG. 3a, where the percentage load p,, is represented on the abscissa, and the output voltage of the comparator 203, designated r is shown on the ordinate. As is represented in FIG. 3a, the output of the comparator v is energized to produce an output voltage, designated V whenever the percentage load, p, is less than the first reference, V from source 212. The voltage V is one which is sufficient to energize the on-off relays 204 of the hood spray. For percentage loads above V (which for the embodiment of FIG. 2 and FIG. 3a is assumed to be 10 percent), the output voltage v of comparator 203 is zero. Thus, for the embodiment shown, the comparator 203 operates responsively to the percentage load 7,, to turn on the hood sprays by means of on-off relays 204 whenever the percentage load is less than 10 percent.

The percent load p is also coupled to a scaling amplifier 207 which produces a scaled, shaped voltage output waveform v, which facilitates operation of the principles of the present invention. FIG. 3b shows a preferred transfer characteristic for the scaling amplifier 207. In preferred embodiments of the present invention, as exemplified in FIG. 3b, the crucial range for interaction of load with vacuum to control the hood sprays is between 10 and 25 percent load. Thus, in FIG. 3b, the crucial cut-offs may be seen to occur at 10 and 25 percent load. For loads below 10 percent, it will be recalled that comparator 203 provides that the hood sprays will be in an on condition; thus, a dont care" condition exists for sealing amplifier 207 below 10 percent load. In order to insure smooth operation, however, it is preferable that for loads below 10 percent, the scaling amplifier 207 produce an output voltage which has continuity with the desired waveform above 10 percent. In FIG. 3b, this voltage is designated V In the range between 10 and 25 percent load, the output voltage v of scaling amplifier 207 linearly decreases from V to zero, and for loads above 25 percent is maintained at zero. The linear decrease in v from 10 to 25 percent load facilitates operation of the present invention because, as the load increases, the stabilizing effect of steam in the hood spray region tends to require less cooling from the hood sprays. Thus, the voltage v which in conjunction with the exhaust vacuum will determine whether or not hood sprays are required above 10 percent load, tends to decrease with increases in loads. A linear decrease is shown for this region in FIG. 3b, but is to be understood that other transfer waveforms may be desired, such as, for example, parabolic, hyperbolic, or exponetial changes in v over a prescribed range in percentage load, p,

The vacuum 11,, is also coupled to a scaling amplifier 208 where it is operated upon for interaction with the scaled voltage signal v The transfer characteristic of scaling amplifier 208 is shown in FIG. 30, wherein the exhaust vacuum h, is shown on the abscissa and the output voltage v,- is shown on the ordinate. In preferred embodiments of the present invention, vacuum as complete as 28 /2 in. Hg. tend not to cause sufficient windage heat to require hood spray cooling. Between 28 V2 and 26 inches of mercury, however, the windage heat tends to increase, and so does the need for the hood sprays. Below 26 inches of mercury, hood spray cooling generally is required below 25 percent load. This vac uum responsive requirement for hood spray cooling is reflected in the transfer characteristic of FIG. 30, for which the output voltage v is zero up to 28 /z inches of mercury, and then linearly increases between 28 /2 and 26 inches, reflecting the increased need for cooling, and levels off at a voltage V, beyond 26 inches of mercury. In this fashion, the output voltage v,- of the scaling amplifier 208 represents a progressively greater need for hood spray cooling as the vacuum in the exhaust hood region becomes less and less perfect. As in the transfer characteristic of FIG. 3b, the linear change shown in FIG. 30 may be supplanted, as desired, with waveforms of varying shapes.

Since the principles of the present invention featue dual interactive control of hood spray cooling in response both to vacuum and to load, the output voltages from scaling circuits 207 and 208 are merged in a combine circuit 209 in accordance with an aggregate transfer characteristic for control of the sprays. In accordance with the principles of the present invention, the combined characteristic, which is shown in FIG. 3d, takes into account the need for cooling both due to the absence of the stabilizing effect of steam (i.e., low load) and the heat produced from windage (i.e., imperfect vacuums). The abscissa in FIG. 3d represents the addition at circuit 209 of the load and vacuum control voltages v, and Vy. On the ordinate is plotted a voltage v the control voltage which, relative to a desired reference, determines whether the hood sprays are on or offin the desired range of load and vacuum. In FIG. 3d, for values of v plus v up to a first level, designated E the control voltage v progresses from zero to some level V In this range, neither the load nor the vacuum is sufficiently low to requirehood spray cooling. Next, in a range of v plus v, from E to E the output control voltage v, is stationary at the level .V because of the increasing effect of v,- and the decreasing effect of v Above E it is desirable to have the sprays off at all times. Accordingly, the transfer'waveform of FIG. 3d

,rnay merely involve a cut off of v, for comparable increases of v,, plus v,-, or alternatively may, be any level below the phantom line at V for increases of v,, plus \"y above The combined vacuum and load control voltage v, is coupled to a comparator 211 where it is compared with a second reference voltage, equal to V in order to determine whether or not the hood sprays should be energized. The transfer characteristic of the comparator .211 is shown in FIG. 32, wherein the control voltage v is plotted on the abscissa and the second relay control voltage v is shown on the ordinate. As may be seen from FIGoSe, the relay control voltage VH2 is binary,

being zero for input control voltages below the reference V,-, and being the relay energizing voltage V for joint load andvacuum control voltages v above the second reference V Accordingly, the second comparator 211 in conjunction with the reference V from source 213 establishes the joint load and vacuum control over the hood spray on-off relays 204, as desired.

In summary, the embodiment of FIG. 2, as represented by the waveforms of FIGS. 3a through 3e, causes the hood sprays to be turned on for start up and for low loads, preferably those below 10 percent load.

For loads between 10 and 25 percent, the question becomes whethersthe load and vacuum together require hood spray cooling, eventhough they might not be sufficient individually to require such cooling. Finally, if

the load is sufficiently high and the vacuum sufficiently effective, hood spray cooling is not required and the relays are maintained in the off condition.

While the embodiment described is operated on the basis of crucial cut-off points being 10 and 25 percent load and 28 /2 and 26 in. Hg. of exhaust vacuum, it is to be understood that those cut-off points are subject to variation, as desired, by those skilled in the art in order to accommodate other generating systems of varying characteristics. Clearly, a given system might feature a predominate effect of either load or vacuum over the other, which of course would require comparable variation in the various transfer characteristics of circuits 207, 208, and 209. Such alteration, however, is believed well within the capability of those skilled in the art.

FIG. 4 shows a schematic circuit diagram of the embodiment of FIG. 2. In FIG. 4, a load transducer 402 and a vacuum transducer 406 respectively sense the present generator load and the present partial vacuum in the exhaust hood region, depicting them in the form of voltage signals p and h,,. The load signal p is coupled to a comparator 403 and to a load scaling amplifier 407. The comparator 403 corresponds to the first comparator 203 of the FIG. 2 embodiment, and serves to compare the percentage load signal p with a voltage reference V, from a supply 412. Accordingly, the output voltage from the operational amplifier 1403, v may be utilized to turn on the hood sprays by means of a hood spray control relay 205. Accordingly, the voltage v is coupled through the emitter stage of a transistor 421 to operate the relay 205. In turn, so long as v,,, is sufficiently large to energize the relay, the closure of the switch of relay 205 energizes the hood sprays. The operational amplifier 1403 of comparator 403 involves various resistors and capacitors selected to produce a transfer characteristic such as shown in FIG. 3a.

The percentage load signal p is also coupled to an input stage of a load scaling amplifier 407, which includes an operational amplifier 1407 and appropriate input and feedback circuitry to produce a transfer characteristic such as shown in FIG. 3b. The output of the operational amplifier 1407, v is coupled to a first input of a combine and compare circuit 409.

The output voltage 11,. from the vacuum transducer 406 is coupled to an input of a vacuum scaling amplifier 408, which in turn includes an operational amplifier 1408 with appropriate input and feedback circuitry. In addition, to scale the vacuum voltage signal for appropriate interaction with the load signal p and thereby to achieve harmonious interaction throughout the circuitry, the scaling amplifier 408 includes variable resistors. By adjusting these resistors appropriately, coordinated operation is insured. The output voltage from the operational amplifier 1408, v is coupled to another input of the combine and compare cir cuit 409. Connected to yet a third input for the combine andcompare circuit 409 is a reference voltage V. from a source 413. The combine and compare circuit 409 includes an operational amplifier 1409 properly biased at its input and feedback circuitry to merge the functions of combine circuit 209 and comparator 211 of FIG. 2. Thus, the emitter voltage of transistor 422, designated v is the control voltage for a relay 204 which operates the hood sprays. Thus, since the various circuits 407, 408, and 409 together embody the transfer characteristics shown in FIGS. 3b through 3e, the

result is operation as previously described in conjunction with the embodiment of FIG. 2.

In summary, the circuit of FIG. 4 duplicates the bifurcated path of the FIG. 2 embodiment to achieve control of hood sprays utilizing both load and vacuum as control parameters. Moreover, proper selection and adjustment of the various resistors and capacitors utilized to bias the corresponding operational amplifiers will produce transfer characteristics similar to those shown in FIGS. 3a through 3e, or, if desired, predetermined variations thereof, In any event, selection of the components is well within the capability of those skilled in the art. Moreover, the various transducers and operational amplifiers set forth in FIG. 4 are embodied as multi-purpose, generally available circuit packages commonly used in the art.

While the detailed embodiment set forth in FIG. 4 is an analog circuit, it is clear that the principles of the present invention may be embodied just as effectively by digital circuitry. For example, any of the voltage quantities referred to herein may be represented by appropriately quantized and coded digital signals for utilization by well known digital circuitry in the same fashion as are the analog signals set forth hereinbefore.

It is to be further understood that all of the embodiments set forth herein are intended to be illustrative of the principles of the present invention, as set foth in the appended claims. Many variations thereof will readily occur to those skilled in the art without departure from the spirit or scope of the principles of the present invention.

What is claimed is:

1. In a turbine generator system having an exhaust hood on at least one turbine and cooling sprays for said hood, hood spray control apparatus comprising:

a. means for measuring the present load of said gen erator;

b. means for measuring the present exhaust vacuum of steam from said turbine; and

c. means responsive to the measured present load and to the present measured exhaust vacuum for selectively activating said cooling sprays.

2. Control apparatus as described in claim 1 wherein said means for selectively activating comprises:

a. first means for activating said sprays when said present load is below a first predetermined level;

b. means for developing a control signal from said present load and said present exhaust vacuum; and

0. second means, responsive to said control signal, for selectively activating said sprays whenever said present load and said present exhaust vacuum are respectively within first and second predetermined ranges.

3. Control apparatus as described in claim 2 wherein said means for developing a control signal comprises:

a. means for developing a first signal directly proportional to exhaust vacuum in said second predetermined range;

b. means for developing a second signal inversely proportional to measured load in said first predetermined range; and

0. means for combining said first and second signals to yield said control signal.

4. Control apparatus as described in claim'2 wherein 4 said first means for activating comprises:

a. a source of a first reference level; and

b. means for comparing said present load with said first reference level.

5. Control apparatus as described in claim 2 wherein said second means for activating comprises:

a. a source of a second reference level; and

b. comparator means for comparing said first reference level with said control signal.

6. Control apparatus as described in claim 2 wherein said first predetermined level is substantially equivalent to a ten percent load.

7. Control apparatus as described in claim 2 wherein said first predetermined range is substantially between 10 and 25 percent load, and said second predetermined range is substantially between 28% and 26 inches of mercury.

8. In an electric generator, apparatus for maintaining the exhaust load region of a low pressure turbine within specified temperature ranges comprising:

a. at least one spray for each exhaust hood for producing a cooling mist in said hood region;

b. means for exhausting steam from said turbine to a condenser means, thereby producing a partial vacuum in said hood region;

0. means for measuring the vacuum in said hood region;

d. means for measuring the present load of said generator; and

e. means responsive to the present load and to the measured vacuum for selectively activating said spray.

9. Apparatus as described in claim 8 wherein said means for selectively activating comprises:

a. first means for activating said spray when said present load is below a first predetermined level;

b. means for developing a control signal from said present load and from measured vacuum; and

c. second means for selectively activating said spray whenever said present load and said measured vacuum are respectively within first and second predetermined ranges.

10. Apparatus as described in claim 9 wherein said means for developing a control signal comprises:

a. means for developing a first signal inversely proportional to load in said first predetermined range;

b. means for developing a second signal directly proportional to vacuum in said second predetermined range; and

c. means for combining said first and second signals to produce said control signal.

11. Apparatus as described in claim 9 wherein said first means for activating comprises:

a. a source of a first reference level; and

b. means for comparing said measured present load with said first reference level.

12. .Control apparatus as described in claim 9 wherein said second means for activating comprises:

a. a source of a second reference level; and

b. comparator means for comparing said first reference level with said control signal.

13. A method of controlling the activation of hood sprays in an electric generator system comprising the steps:

c. selectively activating the hood sprays in response to evaluations of the present load and the present vacuum.

14. A method as described in claim 13 wherein said activating step includes:

a. energizing the hood sprays when the present load is below a first predetermined level; and

b. selectively energizing the hood sprays when the present load and present vacuum are respectively within first and second predetermined ranges.

15. A method as described in claim 14 wherein said step of selectively energizing comprises:

a. developing a control signal from said present load and said present exhaust vacuum;

b. comparing said control signal with a second predetermined level; and

c. energizing the hood sprays when said control signal is at least said second predetermined level.

16. A method as described in claim 15 wherein said step of developing a control signalcomprises: I

a. developing a first signal directly proportional to exhaust vacuum in said second predetermined range;

b. developing a second signal inversely proportional to load in said first-predetermined range; and

c. combining said first and second signals to yield said control signal. r

17. A' method as described in claim 14 wherein said first energizing step includes:

a. developing -a first reference-level; and

b. comparing said present load with said first ence level.

18. A method as described in claim 14 wherein said first predetermined level is substantially equivalent to ten percent load.

19. A method as described in claim 14 wherein said first predetermined range is substantially between '10 and 25 percent load, and said second predetermined range is substantially between 28 /2 and 26 inches of mercury.

20. A temperature stablized power generation system comprising:

a. a turbine generator having high, intermediate, and low pressure segments, at least one segment having an exhaust hood portion and sprays for cooling the region of said exhaust hood portion;

b. means for measuring the present load of said generator;

c. means for measuring the present exhaust vacuum of steam from said turbine; and

d. means responsive to the measured present load and to the presentmeasured exhaust vacuum for selectively activating said cooling sprays.

21. A system as described in claim 20 wherein said means for selectively activating comprises:

a. first means for activating said sprays when said present load is below a first predetermined level;

b. means for developing a control signal from said referpresent load and said present exhaust vacuum; and 6 0. second means, responsive to said control signal for selectively activating said sprays whenever said present load and said present exhaust vacuum are respectively within first and second predetermined ranges.

22. A system as described in claim 21 wherein said means for developing a control signal comprises:

a. means for developing a first signal directly proportional to exhaust vacuum in said second predetermined range;

b. means for developing a second signal inversely proportional to measured load in said first predetermined range; and

c. means for combining said first and second signals to yield said control signal.

23. A system as described in claim 21 wherein said first means for activating comprises:

a. a source of a first reference level; and

b. means for comparing said present load with said first reference level.

24. A system as described in claim 21 wherein said second means for activating comprises:

a. a source of a second reference level; and

b. comparator means for comparing said first reference level with said control signal.

25. A system as described in claim 21 wherein said first predetermined level is substantially equivalent to ten percent load.

26. A system as described in claim 21 wherein said first predetermined range is substantially between and 25 percent load, and said second predetermined range is substantially between 28 /2 and 26 inches of mercury vacuum.

27. A temperature stabilized power generation system comprising:

a. a turbine generator having high, intermediate, and

low pressure segments, at least one of said segments having an exhaust hood portion;

b. at least one spray for each exhaust hood for producing a cooling mist in said hood region;

c. means for exhausting steam from said turbine to a condenser means, thereby producing a partial vacuum in said hood region;

d. means for measuring the vacuum in said hood region;

e. means for measuring the present load of said generator; and

f. means responsive to the present load and to the measured vacuum for selectively activating said spray.

28. A system as described in claim 27 wherein said means for selectively activating comprises:

a. first means for activating said spray when said present load is below a first predetermined level;

b. means for developing a control signal from said present load and from measured vacuum; and

0. second means for selectively activating said spray whenever said present load and said measured vacuum are respectively within first and second predetermined ranges.

29. A system as described in claim 28 wherein said means for developing a control signal comprises:

a. means for developing a first signal inversely proportional to load in said first predetermined range;

b. means for developing a second signal directly pro- 0 portional to vacuum in said second predetermined range; and

c. means for combining said first and second signals to produce said control signal.

30. A system as described in claim 28 wherein said 65 first means for activating comprises:

a. a source of a first reference level; and

b. means for comparing said measured present load with said first reference level.

31. A system as described in claim 28 wherein said second means for activating comprises:

a. a source of a second reference level; and

b. comparator means for comparing said first reference level with said control signal.

32. A system as described in claim 28 wherein said first predetermined level is substantially equivalent to a ten percent load.

33. A system as described in claim 28 wherein said first predetermined range is substantially between and 25 percent load. and said second predetermined range is substantially between 28 /2 and 26 inches of mercury vacuum.

34. A method of operating a generator system having a plurality of turbine generator segments, at least one of which has associated exhaust hood and hood spray apparatus. comprising the steps of:

a. successively starting up and loading said generator;

b. energizing the sprays during startup;

c. evaluating the present load on said system;

d. evaluating the present exhaust vacuum from the exhaust hood region of said system;

e. selectively activating the hood sprays in response to evaluations of the present load and the present vacuum.

35. A method as described in claim 34 wherein said activating step includes:

a. energizing the hood sprays when the present load is below a first predetermined level; and

b. selectively energizing the hood sprays when the present load and present vacuum are respectively within first and second predetermined ranges.

36. A method as described in claim 35 wherein said step of selectively energizing comprises:

a. developing a control signal from said present load and said present exhaust vacuum;

b. comparing said control signal with a second predetermined level; and

c. energizing the hood sprays when said control signal is at least said second predetermined level.

37. A method as described in claim 36 wherein said step of developing a control signal comprises:

a. developing a first signal directly proportional to exhaust vacuum in said second predetermined range;

b. developing a second signal inversely proportional to load in said first predetermined range; and

c. combining said first and second signals to yield said control signal.

38. A method as described in claim 35 wherein said first energizing step includes:

a. developing a first reference level; and

b. comparing said present load with said first reference level.

39. A method as described in claim 35 wherein said first predetermined level is substantially equivalent to ten percent load.

40. A method as described in claim 35 wherein said first predetermined range is substantially between l0 and 25 percent load, and said second predetermined range is substantially between 28 /2 and 26 inches of mercury vacuum.

41. A method as described in claim 35 wherein said first predetermined range is substantially between 10 and 25 percent load, and said second predetermined range is substantially between 28 and 26 inches of 

1. In a turbine generator system having an exhaust hood on at least one turbine and cooling sprays for said hood, hood spray control apparatus comprising: a. means for measuring the present load of said generator; b. means for measuring the present exhaust vacuum of steam from said turbine; and c. means responsive to the measured present load and to the present measured exhaust vacuum for selectively activating said cooling sprays.
 2. Control apparatus as described in claim 1 wherein said means for selectively activating comprises: a. first means for activating said sprays when said present load is below a first predetermined level; b. means for developing a control signal from said present load and said present exhaust vacuum; and c. second means, responsive to said control signal, for selectively activating said sprays whenever said present load and said present exhaust vacuum are respectively within first and second predetermined ranges.
 3. Control apparatus as described in claim 2 wherein said means for developing a control signal comprises: a. means for developing a first signal directly proportional to exhaust vacuum in said second predetermined range; b. means for developing a second signal inversely proportional to measured load in said first predetermined range; and c. means for combining said first and second signals to yield said control signal.
 4. Control apparatus as described in claim 2 wherein said first means for activating comprises: a. a source of a first reference level; and b. means for comparing said present load with said first reference level.
 5. Control apparatus as described in claim 2 wherein said second means for activating comprises: a. a source of a second reference level; and b. comparator means for comparing said first reference level with said control signal.
 6. Control apparatus as described in claim 2 wherein said first predetermined level is substantially equivalent to a ten percent load.
 7. Control apparatus as described in claim 2 wherein said first predetermined range is substantially between 10 and 25 percent load, and said second predetermined range is substantially between 28 1/2 and 26 inches of mercury.
 8. In an electric generator, apparatus for maintaining the exhaust load region of a low pressuRe turbine within specified temperature ranges comprising: a. at least one spray for each exhaust hood for producing a cooling mist in said hood region; b. means for exhausting steam from said turbine to a condenser means, thereby producing a partial vacuum in said hood region; c. means for measuring the vacuum in said hood region; d. means for measuring the present load of said generator; and e. means responsive to the present load and to the measured vacuum for selectively activating said spray.
 9. Apparatus as described in claim 8 wherein said means for selectively activating comprises: a. first means for activating said spray when said present load is below a first predetermined level; b. means for developing a control signal from said present load and from measured vacuum; and c. second means for selectively activating said spray whenever said present load and said measured vacuum are respectively within first and second predetermined ranges.
 10. Apparatus as described in claim 9 wherein said means for developing a control signal comprises: a. means for developing a first signal inversely proportional to load in said first predetermined range; b. means for developing a second signal directly proportional to vacuum in said second predetermined range; and c. means for combining said first and second signals to produce said control signal.
 11. Apparatus as described in claim 9 wherein said first means for activating comprises: a. a source of a first reference level; and b. means for comparing said measured present load with said first reference level.
 12. Control apparatus as described in claim 9 wherein said second means for activating comprises: a. a source of a second reference level; and b. comparator means for comparing said first reference level with said control signal.
 13. A method of controlling the activation of hood sprays in an electric generator system comprising the steps: a. evaluating the present load on said system; b. evaluating the present exhaust vacuum from the exhaust hood region of said system; c. selectively activating the hood sprays in response to evaluations of the present load and the present vacuum.
 14. A method as described in claim 13 wherein said activating step includes: a. energizing the hood sprays when the present load is below a first predetermined level; and b. selectively energizing the hood sprays when the present load and present vacuum are respectively within first and second predetermined ranges.
 15. A method as described in claim 14 wherein said step of selectively energizing comprises: a. developing a control signal from said present load and said present exhaust vacuum; b. comparing said control signal with a second predetermined level; and c. energizing the hood sprays when said control signal is at least said second predetermined level.
 16. A method as described in claim 15 wherein said step of developing a control signal comprises: a. developing a first signal directly proportional to exhaust vacuum in said second predetermined range; b. developing a second signal inversely proportional to load in said first predetermined range; and c. combining said first and second signals to yield said control signal.
 17. A method as described in claim 14 wherein said first energizing step includes: a. developing a first reference level; and b. comparing said present load with said first reference level.
 18. A method as described in claim 14 wherein said first predetermined level is substantially equivalent to ten percent load.
 19. A method as described in claim 14 wherein said first predetermined range is substantially between 10 and 25 percent load, and said second predetermined range is substantially between 28 1/2 and 26 inches of mercury.
 20. A temperature stablized power generation system comprising: a. a turbine generator havinG high, intermediate, and low pressure segments, at least one segment having an exhaust hood portion and sprays for cooling the region of said exhaust hood portion; b. means for measuring the present load of said generator; c. means for measuring the present exhaust vacuum of steam from said turbine; and d. means responsive to the measured present load and to the present measured exhaust vacuum for selectively activating said cooling sprays.
 21. A system as described in claim 20 wherein said means for selectively activating comprises: a. first means for activating said sprays when said present load is below a first predetermined level; b. means for developing a control signal from said present load and said present exhaust vacuum; and c. second means, responsive to said control signal for selectively activating said sprays whenever said present load and said present exhaust vacuum are respectively within first and second predetermined ranges.
 22. A system as described in claim 21 wherein said means for developing a control signal comprises: a. means for developing a first signal directly proportional to exhaust vacuum in said second predetermined range; b. means for developing a second signal inversely proportional to measured load in said first predetermined range; and c. means for combining said first and second signals to yield said control signal.
 23. A system as described in claim 21 wherein said first means for activating comprises: a. a source of a first reference level; and b. means for comparing said present load with said first reference level.
 24. A system as described in claim 21 wherein said second means for activating comprises: a. a source of a second reference level; and b. comparator means for comparing said first reference level with said control signal.
 25. A system as described in claim 21 wherein said first predetermined level is substantially equivalent to ten percent load.
 26. A system as described in claim 21 wherein said first predetermined range is substantially between 10 and 25 percent load, and said second predetermined range is substantially between 28 1/2 and 26 inches of mercury vacuum.
 27. A temperature stabilized power generation system comprising: a. a turbine generator having high, intermediate, and low pressure segments, at least one of said segments having an exhaust hood portion; b. at least one spray for each exhaust hood for producing a cooling mist in said hood region; c. means for exhausting steam from said turbine to a condenser means, thereby producing a partial vacuum in said hood region; d. means for measuring the vacuum in said hood region; e. means for measuring the present load of said generator; and f. means responsive to the present load and to the measured vacuum for selectively activating said spray.
 28. A system as described in claim 27 wherein said means for selectively activating comprises: a. first means for activating said spray when said present load is below a first predetermined level; b. means for developing a control signal from said present load and from measured vacuum; and c. second means for selectively activating said spray whenever said present load and said measured vacuum are respectively within first and second predetermined ranges.
 29. A system as described in claim 28 wherein said means for developing a control signal comprises: a. means for developing a first signal inversely proportional to load in said first predetermined range; b. means for developing a second signal directly proportional to vacuum in said second predetermined range; and c. means for combining said first and second signals to produce said control signal.
 30. A system as described in claim 28 wherein said first means for activating comprises: a. a source of a first reference level; and b. means for comparing said measured present load wIth said first reference level.
 31. A system as described in claim 28 wherein said second means for activating comprises: a. a source of a second reference level; and b. comparator means for comparing said first reference level with said control signal.
 32. A system as described in claim 28 wherein said first predetermined level is substantially equivalent to a ten percent load.
 33. A system as described in claim 28 wherein said first predetermined range is substantially between 10 and 25 percent load, and said second predetermined range is substantially between 28 1/2 and 26 inches of mercury vacuum.
 34. A method of operating a generator system having a plurality of turbine generator segments, at least one of which has associated exhaust hood and hood spray apparatus, comprising the steps of: a. successively starting up and loading said generator; b. energizing the sprays during startup; c. evaluating the present load on said system; d. evaluating the present exhaust vacuum from the exhaust hood region of said system; e. selectively activating the hood sprays in response to evaluations of the present load and the present vacuum.
 35. A method as described in claim 34 wherein said activating step includes: a. energizing the hood sprays when the present load is below a first predetermined level; and b. selectively energizing the hood sprays when the present load and present vacuum are respectively within first and second predetermined ranges.
 36. A method as described in claim 35 wherein said step of selectively energizing comprises: a. developing a control signal from said present load and said present exhaust vacuum; b. comparing said control signal with a second predetermined level; and c. energizing the hood sprays when said control signal is at least said second predetermined level.
 37. A method as described in claim 36 wherein said step of developing a control signal comprises: a. developing a first signal directly proportional to exhaust vacuum in said second predetermined range; b. developing a second signal inversely proportional to load in said first predetermined range; and c. combining said first and second signals to yield said control signal.
 38. A method as described in claim 35 wherein said first energizing step includes: a. developing a first reference level; and b. comparing said present load with said first reference level.
 39. A method as described in claim 35 wherein said first predetermined level is substantially equivalent to ten percent load.
 40. A method as described in claim 35 wherein said first predetermined range is substantially between 10 and 25 percent load, and said second predetermined range is substantially between 28 1/2 and 26 inches of mercury vacuum.
 41. A method as described in claim 35 wherein said first predetermined range is substantially between 10 and 25 percent load, and said second predetermined range is substantially between 28 1/2 and 26 inches of mercury vacuum. 